Some 30-40 million people are living with Human immunodeficiency virus, HIV. Other retroviruses account for many more infections, and emerging infectious diseases are on the rise. Unfortunately, antiretroviral resistance develops in the presence of the selective pressure of drug exposure. Vaccine development has been problematic. A novel, validated target of intervention for retrovirus infection is the virus'dependence on the recruitment of a specific host cell transfer RNA (tRNA). The host tRNA is recruited by viral proteins into the new viral particles. When the virus infects the very next cell, this tRNA becomes the primer for replication of its RNA genome through reverse transcription. Recently, small proteins, peptides of 15 and 16 amino acids, have been selected from vast libraries of peptides for their abilities to bind specifically the one human tRNA, tRNALys3, that is recruited by HIV, and other lentiviruses for priming reverse transcription. Thus, the peptides mimic HIV viral proteins in their specificity for tRNALys3. The long-term objectives of this program are to understand and exploit the dedicated recruitment of human tRNALys3 by HIV, and to develop peptides as tools for designing new small molecule therapeutics that will inhibit the recruitment, and the peptides themselves as putative therapeutics. The experimental specific aims of the revised project are: 1) The peptides bind the anticodon domain of human tRNALys3 (ASLLys3) with high affinity and specificity characteristic of HIV proteins that recruit the tRNA in vivo. The RNA binding properties of those peptides from 20 that have the highest affinities and specificities will be characterized in detail. 2) Peptide affinity and specificity will compete with one or more of the HIV proteins involved in the recruitment of tRNALys3. Using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry, gel mobility shifts, and fluorescence the abilities of the peptides to mimic HIV proteins involved in recruiting the tRNALys3 will be determined. As a result of the two Specific Aims, the HIV protein/htRNALys3 interaction will be elucidated, and peptides will have been developed as proven tools for investigating viral protein/host cell RNA interactions that are critical to virus replication. The discovered peptides could be progenitors of therapeutics and/or tools in the development of small candidate drugs.